Ignition system



Nov. 21, 1939.

w. r L. CARLSON IGNITION SYSTEM Filed Jan. 20, 1959 colLs cm. ANGLES 5ATTORN EY5 Patented Nov. 21, 1939 PATENT OFFICE IGNITION SYSTEM WilburL. Carlson, Rochester, N. Y., assign'or to General Motors Corporation,Detroit, Mich., a corporation of Delaware Application January 20, 1939,Serial No. 251,889

2 Claims.

This invention relates to ignition systems for internal combustionengines and more particularly to ignition systems for internalcombustion engines which drive generators for producing 15 voltages thatare relatively high as compared with the voltages which prevail inautomotive vehicles.

The voltages most frequently used for' automotive vehicles are 6 volts,or sometimes 12 volts. No difllculties are encountered when using this.

10 6 volt ignition coil or 12 volt coil; but when the voltage generatedby the generator driven by the internal combustion engine exceeds 12volts by a substantial amount, for example, if the voltage is 32 volts,the problem is much more difiicult 15 because it is practicallyimpossible to design a theoretically correct 32 volt ignition coil. Ifsuch a coil were designed, the number of primary turns would be so greatthat 1,000 volts or higher Would be impressed across the breaker pointsand primary condenser. If this high voltage were allowed severe arcingwould result. This would seriously interfere with the performance of thecoil and burn up the breaker points. If a large enough condenser wereused to eliminate arcing,

the natural electrical period of the primary circuit would be so slowthat insufficient voltage would be generated in the secondary coil.

In the past the practice has been to use a 12 volt coil in a 32 voltsystem. A series resistance is connected between the 12 volt coil andthe 32 volt source in order to consume the difference in potential. Whenthis is done the coil does not operate efficiently and furthermoretrouble may be caused by early ignition. A comparatively high 5 voltageis generated in the primary circuit at the time the breaker points closethereby causing a spark to jump at the spark gap at the wrong time. Thestrength of this early ignition spark is directly proportional to theimpressed voltage and the turn ratio of primary to secondary turns.

If an attempt is made to reduce the early ignition spark by reducing theturn ratio, poor performance will result due to lower secondary voltageat the time of contact opening, when the regular spark is required. Inorder to produce a satisfactory spark under all conditions of operation,it is necessary to wind the ignition coil with a comparatively high turnratio. But if a high turn ratio is to be used, some method must be usedto reduce the amplitude of primary voltage at the instant of applicationto the coil. More recently this condition has been met to a certainextent by the use of a specially designed choke coil connected in serieswith the primary coil. At the instant the breaker points close, thebattery voltage is subdivided between the series choke inductance andthe inductance of the primary coil. However, most of the voltage isconsumed by the series choke due to its much higher inductance. But whenthe primary current starts to build up, the series choke becomes highlysaturated magnetically and shifts practically all of the battery voltageover the primary coil of the ignition coil.

The object of the present invention is to provide a circuit whereby a 12volt ignition coil may be used efficiently and without any of theaforementioned difiiculties with a system of generation at a highervoltage, such as 32 volts for example. In the disclosed embodiment ofthe present invention I accomplish this object by grounding one of thegenerator commutator bars and I connect the ignition coil primary andthe ignition timer in circuit with this grounded brush.

I so relate the generator to the ignition timer controlling cam that,when the grounded commutator bar is under the positive generator brush,the ignition timer contacts will be in the act of closing, and so that,when the ignition timer contacts are opened, the grounded commutator barwill have moved toward the negative brush a dis tance which is less thanthe full movement required but which is a distance such that the averagevoltage acting on the ignition coil primary will be correct for a 12volt coil, for example. In this way while the generator is impressingthe voltage as high as 32 volts, for example, upon its terminals, thevoltage obtained from the generator for ignition purposes is arelatively lower voltage suitable for a properly designed ignition coil.

Further objects and advantages will be apparent from the followingdescription, reference being had to the accompanying drawing wherein apreferred embodiment of one form of the present invention is clearlyshown.

In the drawing:

Fig. 1 is a diagram which shows the completion of the ignition circuitthrough the timer contacts and the grounded commutator bar at theinstant that the bar is under the positive generator brush.

Fig. 2 is a wiring diagram similar to Fig. 1 showing the interruption ofthe ignition primary circuit at the instant the grounded commutator barhas moved seven bar spaces away from the positive generator brush.

Fig. 3 is a chart of voltages illustrating the operation of the presentinvention.

Fig 4 is a wiring diagram showing the complete starting, generating andignition systems,

which is shown partially in Figs. 1 and 2.

I will now describe the complete engine starting, generating andignition system with refer- 5 ence to Fig. 4. The engine E having aspark plug P drives, through a shaft 20, a generator G and an ignitiontimer T. Generator G is shown as a bi-pole machine. Its armature coilsare not shown in Fig. 4, but it will be understood that they areconnected in a conventional manner with a commutator having bars 22. Oneof these bars is grounded by a connection from the point 23 to ground.Generator G has a positive brush 24 and a negative brush 25. It has ashunt field 5 winding 26 used for generator purposes and a series fieldwinding 21 used only for engine starting purposes. The terminal brushes24 and of generator G are connected with a storage battery B through anautomatic circuit breaker or 20 cut-out relay R. Relay R comprises apair of normally open contacts 30 and 3| which are closed by the actionof an armature, not shown, attracted to the core of an electromagnetaround which are placed a series magnet coil 32 and 26 shunt magnet coil33. When the generator voltage attains a certain value the excitation ofthe coil 33 will be sufficient to effect the attraction of the relayarmature toward its magnet core and cause contact 30 to engage contact3| thereby 30 closing the circuit between the generator G and thebattery B. When the voltage of the generator falls below a certainamount the voltage impressed by the battery on the circuit will effectthe opening of the automatic circuit breaker R, 35 thereby preventingdischarge of battery current through the generator.

The starting of the engine is effected by the closing of a switch Scomprising a movable contact 42 normally held out of engagement withcontact and 4| by a spring 43. When this switch is closed current willflow from the battery to the generator to a circuit including a seriesfield winding 21, thereby causing the generator to function as a motorfor cranking the engine.

The timer T controls the completion and interruption of the ignitionprimary circuit.

Referring now to Fig. 1, the ignition primary circuit includes thegrounded commutator bar, the positive brush 24, the primary winding 60of the ignition coil C, and timer circuit breaker lever 6| which carriesa contact 52 engageable with a grounded contact 53. The contacts 52 and53 are shunted by a condenser 54 which reduces sparking at the contacts.Timer T includes a timer cam driven by the generator shaft 20. Cam 50 isso located upon shaft 20 with respect to the grounded commutator barthat, when grounded bar is under positive brush 24, ignition timer camI0 will have moved clockwise as shown in the drawing, sufficiently toclear the circuit breaker lever whereby a spring 5la causes the lever 5|to move clockwise to bring its contact 52 into engagement with contact53. In other words, the instant the grounded bar is under the positivebrush 24 the ignition primary circuit will be closed through thecontacts 52 and 53. Ignition timer cam 50 is so shaped that when thegrounded bar has moved a predetermined distance clockwise from thepositive brush 24 toward the negative brush 25, the cam50 will engagecircuit breaker lever 5| to separate contact 52 from contact 53, therebyinterrupting the ignition primary circuit. The instant of interruptionof this circuit a voltage is induced in the primary and transformed tohigher voltage in the .6Q0ndary winding 62 of the ignition coil C. Asparking impulse is thereby induced which is conveyed by wire connectedbetween the secondary 63 and the spark plug P of the engine therebyigniting the fuel mixture at the proper instant in the cycle ofoperation of the engine.

The predetermined distance through which the grounded commutator barmoves during the closing period of the ignition timer depends upon therelative voltages of the ignition coil and of the generator. I havefound, for example, when using a 12 volt coil with a 32 volt generator,that satisfactory ignition voltage is obtained from the generator if,during the closing period of the ignition primary circuit, the groundedcommutator bar moves away from the positive generator brush an angulardistance equivalent to seven commutator bar spaces.

In the particular embodiment of the invention disclosed in thisapplication, I have chosen a generator in which there are nine barspaces between the positive and negative brushes. I have thereforenumbered these bars 9, I, 2, 3, 4, 5, 6, I, 8, 9, beginning with numeral9' for the bar under the positive brush 24, and 9 for the bar under thenegative brush 25. The generator armature coils are designated by A andalso designated by numerals I to 3 inclusive. The angular relationsbetween the bars and coils are shown in the chart of Fig. 3. As the barsare 20 apart, the nine bar spaces make up the 180 or half circle betweenthe positive brush 24 and the negative brush 25. For purposes ofcalculation, the coil angles are not the same as the bar angles. Asthese coils may be considered as being concentrated half way between thecenter lines of adjacent commutator bars it is apparent that, as shownin the bottom line of the figures of the chart, Fig. 3, the spacings ofthe armature coils with respect to the center line of the bar marked 9',are 10, 30, 50, etc., up to 170. In the chart, Fig. 3, curve 10represents individual coil voltages. It is depicted as the portion of asine wave. Curve 13 represents the summation of individual coil voltagesfrom the negative of the positive brush. Curve 14 represents the averagevoltage acting on the ignition circuit.

Curves 10, I4 and 13 are plotted from the following calculations whichare based on the following premises: As previously explained, it will beunderstood that both the positive and the negative brushes of thegenerator are insulated from each other and from the frame of the enginewhich together with the generator forms a unitary power plant. One ofthe commutator bars is grounded. There will, therefore, be a differencein potential between any one of the main brushes and the frame of thegenerator. One side of the ignition circuit is grounded to the frame ofthe generator and the other side of the ignition circuit is connected toone of the insulated main brushes (positive brush 24) as shown in thedrawing.

The breaker points are timed to close at the in-. stant when thegrounded bar is under the main brush 24 which has one side of theignition circuit connected to it. Therefore, at this instant, there willbe zero volts impressed on the primary coil 60 of the ignition coil C.This is shown in Fig. 1. At a predetermined time later the groundedcommutator bar has moved away from the main brush as shown in Fig. 2.Any instant after the grounded bar moves away from the main brush 24there is a potential difference across the ignition circuit and currentstarts to flow. The

amplitude of the voltage impressed on the ignition circuit depends onhow many bar spaces the grounded bar has taken from the main brush 24;in other words, upon the number of armature coils 5 included between themain brush and the grounded bar. Assuming that the breaker points aretimed by the cam 50 to open when there are seven armature coils includedbetween the main brush and the grounded bar, the maximum in- 10stantaneous voltage on the ignition circuit will be equal to the sum ofthe voltages generated in each of the included armature coils. In orderfor this system to function properly, the average value of the voltagebetween zero and the maximum volt- 1 age at the time of break must beequal to the voltage rating of the ignition coil. That is, if a 12 voltignition coil is used, then the average voltage impressed on the coilbetween the time the breaker points close and open must be 12 to go 14volts. Curve H of Fig. 3 shows that the average voltage is 14 volts atthe time the grounded commutator brush has moved seven bar spaces awayfrom the positive brush 24.

In order to simplify the calculation of the data 25 from which curve 10,I4 and I3 were plotted it is assumed that sinusoidal voltages aregenerated in the individual coils of the generator armature. Alsoassuming that there are nine (9) coils included between positive andnegative brushes, the 30 angle of the center-line of each armature coilfrom the main brush will be as follows:

Electrical degrees between positive and negative brush=180 3 Anglebetween coils:

Angle between positive brush and center-line of first coil=10 This isshown in Fig. 3.

50 e=E sin where ,:the electrical angle of the center of the coil fromneutral or zero degrees. See Fig. 3.

The voltage generated by each coil is calculated and shown in Table 1.

Table 1 Coil Coil Sm of 0011 No. voltage angle angle Sin 10 0. 1736 0.173612 01 30 .5000E e2 50 7650 7650B 6: 70 9397 .9397E e4 90 1. l. OOOOEe 110 9397 9397E ea 130 7660 766013 61 150 5000 .5000E es 170 .1736.1736E en Let Eo=the total voltage between brushes. Then Eo=61+e2+e3+e4+69 (1) or the sum of all the individual coil voltages.

By an inspection of Table 1 we get for the summationEo=2E(.1736-|-.5000+.7660+.9397) (2) Eo=4.758E+E=5.75BE (3) Assuming thetotal voltage E0 across the brushes to be equal to 36 volts, we get thefollowing by substituting 36 for E0 in Equation 3 Then E= =6 25 volts(5) E 35.850 total As the grounded commutator bar moves from thepositive to the negative brush, the maximum instantaneous voltage acrossthe ignition coil is first zero. One bar from neutral the voltage is1.085 volts. Two bars from neutral the voltage is (1.085+3.125)=4.21 andso on all the way around the commutator. Or in general Where E=themaximum instantaneous voltage impressed on the ignition circuit; or thesummation of any number of the individual armature coil voltages.

The following Table #3 shows the maximum instantaneous voltages E1, E2,E3, etc., from the positive to negative brushes.

Table 3 E1: 1.085 E2: 4.210 E3 9.000 E4=14.800 E5=21.050 Ee=26.850E7=31.640 Ea=34.'765 E9=35.850

and so on all the way around the commutator. Or in general mi n+1 (7)Table 4 shows values of E0 from E==0, to Ea==9 .5425 volts Table 4Average voltages impressed on the ignition circuit Number of bar fromzero Up until this time it was assumed that there was no armaturereaction. According to the laws of armature reaction the magnetic fieldshifts in the direction of rotation when the machine generates, butshifts against the direction of rotation when motoring.

In the chart, Fig. 3, arrow pointing toward the right designatesclockwise rotation corresponding to the manner of rotation indicatedwith respect to the operation of the generator as shown in Figs. 1 and2. Curves II shows individual coil voltages when the generator isoperating as a motor. It will be observed that the coil voltage hasshifted to the left. Curve 12 represents individual coil voltages whenthe machine is generating at normal speed. It will be observed thatarmature reaction has shifted the individual coil voltage toward theright. It is therefore apparent that the eifect of armature reaction isto automatically meet the demands for voltage under starting and runningconditions. That is, the eifect of armature reaction when starting, willtend to raise the average voltage impressed on the ignition coil primary60 and thus compensate for the low starting voltage. It will beunderstood that the voltage impressed on the ignition coil is low whenstarting on account of the drain on the battery due to the startingoperation. Armature reaction will have the opposite effect upon theignition circuit during generating since the average voltages will belowered to compensate for high charging voltages.

Instead of employing a generator having insulated positive and negativebrushes and grounded commutator bar, the same results could be obtainedby using a generator having a grounded brush and having a commutator barconnected to an insulated collector ring from which current is takenfrom a. brush and conveyed to the ignition coil winding 60.

The advantages of my new system are as follows: No series resistance isrequired because correct voltage is supplied to the coil. No seriesreactance is required because zero potential is impressed on the coilswhen the primary circuit is closed by the breaker points. The wiring ofthe system has been simplified, hence it may be constructed at lowercost and there will be less liability for trouble. The system givesimproved performance over a system in which an attempt is made to use .a12 volt coil in a 32 volt system because the coil is operatingefiiciently.

I will now discuss the limitations to the satisfactory operation of anignition system constructed in accordance with the present invention.

This system will not operate satisfactorily with all combinations ofnumbers of generator poles and number of cylinders. The combinationswhich are correct are those in which the number of cylinders divided bythe number of poles in the generator will give either a whole and evenquotient as a result of the division or a fraction which has an evennumber as a denominator reduced to lowest terms:

Number of cylinder-s numb" Number of poles Number of cylinders 1 Numberof poles even number Example of correct combination 1 (cylinder) 1 6(poles) 6 Example of incorrect combination 4 (cylinders) 2 (poles) 3 Inorder for this system to give good performance the following conditionsmust be met.

The number of poles or the generator R. P. M. or the combination of bothmust be of a value that will allow the ignition coil to become satu- Rii=g(1-e L s The constants of an ordinary 12 volt system areapproximately as follows:

E=12 volts L= .02 henries, inductance R=3A ohms Assuming that we take Ltseconds for the minimum saturation time and substituting these valuesin Equation 8 we get:

=3.53X.632=2.235 amperes This is the current that a standard 12 voltcoil will take on 12 volts when L tseconds Since L=.02 and R=3.4 we haveFrom this it will be seen that if the maximum that the coil would drawat 12 volts on stall is then the a'mprs at a saturation time of t .00589seconds 5 will be 2.235 amperes, or (2.235/3.53) 100= 63.2% of max.

E current R The time (t) allowed for the coil to saturate, by agenerator of any number of poles and at any speed is For example, if thegenerator has 6 poles and operates at 1800 R. P. M., then substitutingthese values in Equation 9 gives This shows that when the maximumvoltage between brushes is 36 volts and the number of poles are (6) six,the maximum allowable speed will approximately be 1800 R. P. M. Or ingen- 25 eral t =.00556 seconds 1 and t= 60 During the cranking of theengine the ignition circuit includes the following: Battery B, switch 8,series field 21, primary winding 60 of coil C,

timer '1, ground to the commutator bar grounded at 23, armature ofgenerator G, brush 25 and return to battery B.

While the form 01' embodiment of the present invention as hereindisclosed constitutes a preferred for'm, it is to be understood thatother forms might be adopted, all coming within the scope of the claimswhich follow.

What is claimed is as follows:

1. An ignition system for prime-mover dynamo power plants comprising, incombination, a direct current generator, an internal combustion enginedriving the generator, an ignition coil designed to operate on lowervoltage than the generator terminal voltage and having a secondarywinding connected with the engine spark plug and primary windingconnectible with the generator, a circuit including the primary windingand a varying number of generator armature coils, and an engine-drivenignition timer circuit breaker for making the ignition primary circuitwhen there are zero generator armature coils included in the circuit andfor breaking the ignition primary circuit when there are a predeterminednumber of generator armature coils included in the circuit (less thanthe full number of armature coils between generator terminal brushes),the predetermined number of armature coils being such that the averagevoltage impressed upon the ignition coil is approximately equal to therated voltage of the ignition coil.

2. An ignition system according to claim 1 in which the generator isprovided with a grounded commutator bar, in which one end of theignition coil primary is connected to a generator terminal brush, inwhich the other end of the ignition coil primary is connected to theignition timer circuit breaker which is grounded, and in which theengine driven timer cam is so constructed and related to the generatorthat the circuit breaker completes the ignition coil primary circuitwhen the grounded commutator bar is under the said terminal brush oi thegenerator and that the circuit breaker interrupts the ignition coilprimary circuit when the grounded bar has moved a predetermined angulardistance away from the said terminal brush of the generator, thepredetermined distance being such that the average voltage impressedupon the ignition coil is approximately equal to the rated voltage ofthe ignition coil.

WILBUR L. CARLSON.

